Electrical circuit breaker



p 23, 1969 L. w. BRACKETT, SR 3,469,222

ELECTRICAL cIRcun' BREAKER 3 Sheets-Sheet 1 Filed Jan. 26, 19s? .Zhvezmfar el 23, 1969 Q L. w. BRACKETT, sn 3,469,222

ELECTRI GAL CIRCUIT BREAKER Filed Jan. 26, 1967 3 Sheets-Sheet z I i fl I J. PM 1' i J, 11

I 1 1I [L 1'? W 4.;

p 23, 1969 L.W.BRACKE1"T, SR 3,469,222

ELECTRICAL CIRCUIT BREAKER Filed Jan. 26. 1967 3 Sheets-Sheet 5 United States Patent 3,469,222 ELECTRICAL CIRCUIT BREAKER Lawrence W. Brackett, Sr., Georgetown, Mass., assignor to Wood Electric Corporation, Lynn, Mass., 21 corporation of Massachusetts Filed Jan. 26, 1967, Ser. No. 611,887 Int. Cl. H01h 71/16 U.S. Cl. 337-74 2 Claims ABSTRACT OF THE DISCLOSURE An automatic circuit breaker of the trip free type has two fixed contacts and two corresponding parallel spring contacts side by side. A push button operator has hinged to its inner end a rod having at its swinging end rollers which bear against the spring contacts on one side and which swinging end is rigidly connecting. on the other side with a link to one arm of a spring biased lever having a catch on a second arm. A bimetal element bridges the spring contacts and reaches from their fixed side towards the catch which it normally holds with its swinging side forming a latch. The swinging end of the operator rod is normally, with the push button depressed, over center and holds the spring contacts closed. On pulling back the push button the rolls on the operator rod release the spring contacts and they open. Upon overload, the latch of the heated bimetal element releases the catch of the biased two armed lever and permits the spring contacts to open. The circuit breaker cannot be held closed, or reclosed, so long as the bimetal strip remains heated and hence in catch releasing position. The bimetal element can be adjusted to swing its latch end similarly to its motion upon overload heating.

BACKGROUND OF THE INVENTION Field of the invention The invention relates to circuit makers and breakers responding to thermal currents by way of a latch trip.

Description of the prior art Circuit breakers of this type if intended for use in critical circuitry, must be absolutely reliable. In many instances which may also involve high current loads in critical positions, there is further required adaptation to severely restricted space, so-called miniaturization.

Circuit breakers of the general type of Patent No. 2,613,296 are suited for adaptation to the above indicated requirements. Such adaptations are described in the present inventors Patent No. 2,958,749 of Mar. 13, 1958 and in the Patent No. 2,961,513 of Nov. 18, 1958 to Morris B. Wood.

These prior constructions, while satisfactory for many purposes, exhibit detrimental properties under severe operating conditions. It was found, for example, that the roller movement between the push button operator and the latching mechanism is not absolutely reliable. It is difiicult to avoid wear of four rollers and to keep them in alignment, which causes erratic breaker operation. Also, previously suggested modes of adjustment of bimetal elements within breakers of this type have the disadvantage of affecting the releasing movement of the bimetal latch, which aifects the accuracy of response.

SUMMARY OF THE INVENTION Circuit breakers according to the invention, similar to the above-indicated type of trip free breakers of the prior art, incorporate fixed and movable spring contacts, a swinging bimetal structure forming a latch at the free end, a biased two-armed lever having on one side a catch, and

ice

an operator such as a push button with a swinging rod that operates the spring contacts by way of a roller arrangement at its free end. The improvements according to the invention involve a rigid link pivotally connected at one end of the roller pivot at the free end of the operator rod, and at the other end to the other side of the biased catch lever. The bimetal element is supported by a yielding mounting portion. An adjusting screw that is threaded into a part of the housing bears against the mounting portion obliquely to the general extension of the bimetal strip, so that on being turned. the screw causes the catch end of bimetal strip to swing in a path similar to that which it described on being heated. No external adjusting force is applied to the bimetal element proper.

In this manner, the object of permanent alignment of the biased catch lever with the cooperating components at the respective ends of its arn1s--the operator rod at one end and the bimetal latch at the other end-is more securely established, preventing erratic operation in that area. Furthermore, pairs of rollers with linear pressure regions subject to wear at a critical point are avoided. The stucture as a whole is simple, rugged, inexpensive in manufacture and assembly, and reliable even if built to very small size.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of a circuit breaker according to the invention;

FIG. 2 is a section on lines 22 of FIG. 1 with the complete breaker mechanism in place;

FIG. 3 is a section on lines 3-3 of FIG. 2;

FIG. 4 is a section on lines 4--4 of FIG. 2;

FIG. 5 is a section on lines 5-5 of FIG. 2;

FIG. 6 is a fragmentary section on lines 66 of FIG. 5;

FIG. 7 is a fragmentary elevation similar to FIG. 2 showing the circuit breaker in normally open positions; and

FIG. 8 is a fragmentary elevation similar to FIG. 7 showing the circuit breaker in trip-free position with the button held in depressed position.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1 to 6, the present circuit breaker has a split housing 10 which provides supporting means for the breaker mechanism and consists of two shells 11, 12 which secure between them a barrier sheet 15 by means of four screws such as indicated at 16 in FIG. 2, in the manner described in the above-mentioned prior art disclosures. A cover plate 18 is fastened to the housing by means of the screws 16, has a registering tab 18.1, and carries a threaded sleeve 19 for securing the circuit breaker to a panel. The sleeve 19 also guides the plunger 20 of the operator push button 21. The push button plunger 20 has two ears (one of which is indicated at 20.1 of FIG. 2) between which is fixed the operator rod pivot pin 22.

Fixed contacts 31 and 32 (FIGS. 2 and 5) are carried by contact bars 33, 34 which are confined in the insulating housing, ending in offset terminals 33.1, 34.1, with appropriate provisions for tying into circuit wiring. Movable contacts 41, 42 (FIGS. 2 and 5) are fastened to contact springs 43 and 44. These contact springs are fastened, each to one shell of the housing, by means of the retainers 43.1, 44.1 and the bimetal mounting portions 45, 46. Between the mounting portions and the housing shells are adjustment bars 48, 49 (FIGS. 3). These contact spring and bimetal assemblies are secured to the respective housing shell by means of screws 51, 52, 53, 54 (FIGS. 2 to 4). For the purpose of increasing the current carrying capacity, braided conductors such as indicated at 44.2 for contact spring 44, may be mounted between the contact springs and the retainers 43.1 and 44.1.

The bimetal element 60 (FIG. 3) is U-shaped and has two legs 61, 62 and an end piece 63. The legs are curved as indicated in FIG. 2. The end piece 63 has an extension tab 63.1 and carries a latch plate 65.

In addition to the mounting screws 51-54, the bimetal assembly has two adjustment screws, one of which is indicated at 57 in FIG. 2. These set screws are accessible through openings 59 and held in the above-mentioned adjustment bars 48 and '49 into which they are threaded. The bimetal mounting portions 45, 46 are capable of yielding somewhat at their free ends on which the screws 57 bear approximately perpendicular, to the pressure exterted by screws 57 thereby swinging the bimetal strips proper about the flexible ends of these portions. Such adjustment causes the opposite ends of the bimetal strips to swing in paths that are approximately identical to the paths which these ends describe upon thermal deformation of the bimetal strips, and hence to the swing of catch 65.

The controlmovement assembly has a two-armed catch lever 71 pivoted on a pin 72, the ends of which are secured to the respective housing shells. One arm 71.1 of the lever has a catch tooth 73 which engages the latch plate 65 of the bimetal element when the breaker is in normally closed position. A spring 74 biases the catch lever 71 to rotate in clockwise direction as indicated by arrow a in FIG. 2. The other arm 71.2 of the catch lever 71 carries a pin 76 on which are pivoted two links 81, 82 (FIGS. 2 and 4). The other ends of these links rotate on a pin 85 on which is also pivoted, intermediate the two links 81, '82, the swinging end of the above-described operator rod 23. Two rollers '87, 88 are pivoted on the pin 85 on the outsides of the links 81, 82. As shown in FIGS. 2 and 4, the rolls 87, 88 contact the contact springs 43, 44 respectively.

The operation of the above-described circuit breaker is O as follows.

In normally closed position as shown in FIG. 2, the operator push button 21 is depressed and rollers 87, 88 press against the contact springs 43, 44 being held on the other side by the links 81, 82 and the catch lever 71 by way of its tooth 73 and the latch bar 65 of the bimetal element. A current path is established from terminal 33.1 through fixed contact 31, movable contact 41, contact spring 43, the U-shaped bimetal element with its bridging portion 63, second contact spring 44, fixed contact 32, contact bar 34 and terminal 34.1.

For opening the circuit breaker, the push button is pulled out into the position shown in FIG. 7. The movement of pin 85 from over center (as in FIG. 2) releases rolls 87, 88 with rod 23, links 81, 82 and catch lever 71. The withdrawal of rolls 87, 88 permits the spring contacts 41, 42 to open.

Upon an overload occurring in the circuit of which the breaker is a part, the bimetal element is heated, its arms 61 and 62 bend upwardly as shown in FIG. 8 and the latch bar 65 releases the catch tooth 73. Thereupon the catch lever 17 is turned by the force of the spring contacts against the biasing spring 74, and the contacts open. It will be evident that this tripping operation takes place if overload occurs while the button is held down. If an overload exists while the circuit breaker is open, pressing of the button is unable to close the contacts.

It will now be evident that the linkage 81, 82 excludes uncertainty of operation, and that the present mode of adjusting the latch serves the same purpose.

I claim:

1. A circuit breaker having contact means fixed to a support and two movable spring contact means side by side;

a swinging bimetal element with a latch at the free end;

a biased two-armed lever having at the end of the first arm a catch for the bimetal latch;

an operator to which is hinged a rod swinging between the spring contact means and the lever and having a pivot pin on the swinging end for carrying means to engage the spring contact means; and

a rigid linkage between the swinging end of the operator rod and the second arm of the two-armed lever, for securing positive relation between the operator and the catch of the lever, said rigid linkage having two parallel links each with one end pivoted on said pin on either side of the swinging rod, said second arm of the two-armed lever being pivoted between the other ends of the parallel links, and said means to engage the spring contact means including two rollers pivoted on the pin on the outside of respective links and rollingly contacting respective ones of the two spring contacts.

2. Circuit breaker according to claim 1 wherein, according to a further improvement, the bimetal element includes:

a heat insensitive mounting portion fixed at one end region to the support, with the other end region obliquely extending therefrom, and having a free resilient region between the said end regions,

a thermal current sensitive bimetal strip portion fixed to and extending obliquely from said other end region of the mounting portion approximately at right angles to said fixed end region of the mountin portion and to said swinging rod, towards its swinging free end with the said latch, and

an adjusting screw threaded in the support engaging and bearing on the said other end region of the mounting portion approximately perpendicular, upon adjustment swinging of the latch of the sensitive strip portion in a path similar to the heat responsive excursion of the latch.

References Cited UNITED STATES PATENTS 2,673,267 3/1954 Rowe et a1 ZOO-116.2 2,798,918 7/ 1957 Gelzheiser 200116.1 2,961,513 11/1960 Wood 2001l6.1

BERNARD A. GILHEANY, Primary Examiner R. L. COHRS, Assistant Examiner 

